/Engine/Source/Editor/SequencerCore/Public/MVVM/Views/SOutlinerView.h
Called when a node has been expanded or collapsed
void OnExpansionChanged ( [TWeakViewModelPtr](API\Editor\SequencerCore\TWeakViewModelPtr)< [IOutlinerExtension](API\Editor\SequencerCore\MVVM\Extensions\IOutlinerExtension) > InItem, bool bIsExpanded )